Observational properties of low-redshift pair instability supernovae

Context. So-called superluminous supernovae have been recently discovered in the local Universe. It appears possible that some of them originate in stellar explosions induced by the pair instability mechanism. Recent stellar evolution models also predict pair instability supernovae from very massive stars at fairly high metallicities (i.e., Z ~ 0.004). Aims. We provide supernova models and synthetic light curves for two progenitor models, a 150 M⊙ red supergiant and a 250 M⊙ yellow supergiant at a metallicity of Z = 0.001, for which the evolution from the main sequence to collapse and the initiation of the pair instability supernova itself has been previously computed in a realistic and self-consistent way. Methods. We use the radiation hydrodynamics code STELLA to describe the supernova evolution of both models in a time frame of about 500 days. Results. We describe the shock-breakout phases of both supernovae, which are characterized by higher luminosity, longer duration, and a lower effective temperature than those of ordinary Type IIP supernovae. We derive the bolometric, as well as the U, B, V, R, and I, light curves of our pair instability supernova models, which show a long-lasting plateau phase with maxima at Mbol ≃ −19.3 mag and −21.3 mag for our lower and higher mass models, respectively. While we do not produce synthetic spectra, we also describe the photospheric composition and velocity as a function of time. Conclusions. We conclude that the light curve of the explosion of our initially 150 M⊙ star resembles those of relatively bright type IIP supernovae, whereas its photospheric velocity at early times is somewhat lower. Its 56Ni mass of 0.04 M⊙ also falls well into the range found in ordinary core collapse supernovae. The light curve and photospheric velocity of our 250 M⊙ models has a striking resemblance to that of the superluminous SN 2007bi, strengthening its interpretation as pair instability supernova. We conclude that pair instability supernovae may occur more frequently in the local universe than previously assumed